The present invention relates to precision spindle assemblies and in particular to a spindle shaft for coupling to a bearing assembly.
Spindle assemblies for data disk drive devices have data disks attached and rotate the disks at fairly high rates compatible with reading and writing data and to reduce data access time. Precision spindle assemblies are required to rotate the disks accurately because of ever increasing data track densities and increasing linear bit densities. As these data densities continue to rise, particular importance is placed on the spindle performance as measured by the magnitude of the repeatable radial run-out. With high run-out, the data reading and writing heads need to be moved radially to follow the data tracks as the disks rotate. Radially moving the head to follow the data track becomes more and more complex as greater accuracy is required with increased data densities. One of the greatest contributors to run-out is the clearance between the outer diameter of the spindle shaft and the inner race of the bearing assembly.
Prior approaches to reduce the run-out involve the use of press fits between bearing assemblies and shafts, shims, or the use of adhesives to bond bearings to shafts while oriented in precision fixtures. The data disks are then formatted. Further efforts to reduce the run-out included selective assembly techniques such as the use of matched pairs of bearing assemblies. These procedures are expensive and time consuming.
In United Kingdom Pat. No. 548,690, U.S. Pat. Nos. 3,776,651 to Peter et al. and 608,178 to Cock, expansion of sleeves to grip workpieces, hubs and rails respectively are shown. In U.S. Pat. No. 3,670,315 to Fowler, an expandable collet attached to a spindle is expanded to hold a memory disk assembly to the spindle. Expansion techniques are not known to have been used to secure a spindle shaft to the inner races of a bearing assembly.